1. Field of the Invention
Aspects of the present invention relate to machine vision systems, and more particularly, to machine vision systems for locating rectangular shaped objects.
2. Description of Background Information
In many manufacturing processes, machine vision systems are used to automate the assembly and production process. In the semiconductor industry, for example, machine vision systems are commonly used in mounting and inspecting electronic components. In particular, electronic devices, such as semiconductor chips and resistors, are often mounted on the surface of printed circuit boards. The electronic devices, called surface mounted devices (SMDs), are mounted on the circuit board using machine vision based guidance to ensure that the device is placed at the proper position and in the proper orientation on the circuit board.
An initial step in mounting SMDs using a machine vision system involves capturing an image including the SMD and then locating the SMD in the image. Locating and finding the orientation of the SMD may be performed with a search algorithm such as the well known normalized correlation search algorithm. Before the normalized search can locate a particular SMD, however, it must be trained for the SMD. Typically, training involves inputting an abstract model to the search algorithm, thus giving the search algorithm a description of the device it is supposed to locate.
One important facet of the SMD abstract model is a description of the body of the SMD. Often the position and orientation of an SMD body serve as an indication of the position and orientation of more critical elements of the SMD, such as leads or solder balls on the SMD.
Many SMDs have generally rectangular shaped bodies. Accordingly, the abstract model of these rectangular SMDs contains length and width information of the rectangle.
The descriptions of the SMD bodies may come from a variety of sources. CAD (computer aided design) data, if available, may be used. Alternatively, an operator may manually measure the dimensions of the SMD. CAD data, however, is often unavailable, and manual measurement can be clumsy and imprecise.
Accordingly, there is a need in the art to improve the process of locating and characterizing rectangular shaped bodies in an image.